Broadly, this invention relates to a thermal stamping apparatus for stamping or transferring a film to the outer surface of an object utilizing a heat transfer roll, and more particularly to such an apparatus wherein the amount of heat transferred by the roll to the film during the stamping operation can be maintained within a set range.
Stamping devices are known for transferring a film from a carrier or backing member to the outer surface of an object utilizing a heat transfer roll. Generally, the object to be stamped is mounted to a rotary jig and a carrier or backing member carrying the film to be transferred is fed between the transfer roll and the object as the jig rotates. When the film is pressed against the surface of the object while heated by the transfer roll, a heat sensitive adhesive layer on the film is activated and attaches the film to the outer surface of the object. In order to provide uniform and continuous stamping, it is necessary to maintain the amount of heat transferred to the film within an optimum range at all times.
Prior art devices are known that detect the surface temperature of the transfer roll utilizing a temperature sensor which controls a heater adapted to heat the transfer roll. This arrangement is intended to maintain the surface temperature of the transfer roll within a predetermined range. However, when the surface temperature of the transfer roll deviates from the pre-determined range, a time lag is experienced between the detection of the deviation and the response of the heater. Further, an additional time lag is experienced while the transfer roll acquires the desired temperature range. during the time lag, defective stamping may occur.
Since the amount of heat transferred from the transfer roll to the film is attributed to direct heat conduction, the amount of heat transferred is determined by multiplying the surface temperature of the roll by the time period during which the film remains in contact with the transfer roll. Therefore, it is possible to maintain the rate of heat transfer at a constant even when the surface temperature of the roll deviates from the pre-set range by varying the speed at which the transfer roll traverses the surface of the object.